"The leader is the only person they respect and listen to," civil rights activist, Shehu Sani, who was involved in past negotiations with the terrorists, told Nigeria's Premium Times. "Any statement that is not coming from the leader of the group cannot be said to be credible and will not be complied with by the group member."

Boko Haram, who fights against the westernisation of Nigeria and aims to impose their version of sharia law in the country, declared an Islamic caliphate in Gwoza, along the Cameroon border, in August 2014. The group has been raiding several cities in the north of the country in a bid to take control of more land.

A woman in a sit-in protest for the schoolgirlsReuters

Borno, Yobe, and Adamawa states, where the militants usually carry out their attacks, have been under a state of emergency since May 2013.

The Chibok mass kidnapping has caught the attention of the international media, prompting prominent politicians and celebrities to publicly condemn the abduction.

Hundreds of people have joined the Twitter campaign #BringBackourGirls to raise awareness of the issue, while countries, such as Britain, France, and the US, are helping Nigerian troops in the search.